1. Technical Field
This invention relates generally to bearing assemblies. In particular, a bearing assembly of the present disclosure may be employed, e.g., in the down-hole drilling field, and may be disposed in a bottom hole assembly (BHA) to accommodate rotational motion of a drill bit relative to an elongate upper portion of a drill string.
2. Description of Related Art
Often in down-hole drilling operations, a down-hole drilling motor is suspended from the lower end of a string of drill pipe. A drilling fluid may be transmitted through the drill string and circulated through the drilling motor to induce rotation of a drill bit. The rotating drill bit engages a subterranean formation to produce a borehole therein.
To support the rotation of the drill bit, and to reduce frictional wear caused thereby, a bearing assembly is generally provided with the drilling motor. These motor bearing assemblies are subject to axial or thrust loads. For example, a least a portion of the weight of the drill string may be placed on the bit to enhance the drilling, and this weight on bit (“WOB”) passes through the bearing assembly. Also, expected axial loads include forces generated as the drill bit engages the formation, and bounces off the bottom of the borehole. In certain conventional down-hole drilling motors, vertical thrust bearings are provided, which include hard bearing surfaces such as diamond studs. These hard bearing surfaces are referred to in this application as polycrystalline diamond compact bearings (“PDC bearings”). A more detailed description of PDC bearings may be found, e.g., in U.S. Pat. No. 4,620,601 to David D. Nagel, the entire content of which is incorporated herein by reference. The bearings are also subject to radial loads, e.g., loads generated as the sides of the bit engage the formation. Radial loads are particularly relevant in directional or horizontal drilling operations.
In the drilling environment, the radial space available for equipment is limited by the size of the hole to be drilled. Additionally, the axial space available may also be limited by factors such as the necessary turning radius of the bit in a directional drilling operation. Accordingly, to increase the load carrying capacity of a bearing in a drilling environment, consideration must be taken to accommodate the expected loads in the space available.